Yield curve control is different in one major respect from QE, the trillions of dollars in bond-buying that the Fed pursued during the Great Recession. QE deals in quantities of bonds; YCC focuses on prices of bonds. Under QE, a central bank might announce that it plans to purchase, for instance, $1 trillion in Treasury securities. Because bond prices are inversely related to their yields, buying bonds and pushing up their price leads to lower longer-term rates.

Under YCC, the central bank commits to buy whatever amount of bonds the market wants to supply at its target price. Once bond markets internalize the central bank’s commitment, the target price becomes the market price—who would be willing to sell the bond to a private investor for less than they could get by selling to the Fed?